This invention relates to turbomachines and more particularly to an airfoil mounting assembly in a gas turbine engine.
While not limited thereto, this invention has particular utility when utilized in conjunction with a gas turbine engine having airfoils such as fan outlet guide vanes and stator vanes. Stator vanes, for example, each can typically include an integral mounting platform at the radially outer end thereof which is fastened to a cylindrical stator casing by retaining rings or by a plurality of mounting bolts. The vanes can have root portions of complex shapes such as the fir tree or dovetail type, which fit complementarily shaped slots in an inner stator supporting ring. Vanes having integral platforms and specifically shaped roots have been considered essential in the prior art to insure accurate alignment and positive retention of the vanes in the stator casing.
Furthermore, modern aircraft turbine engines are becoming shorter in length which requires closer spacing of the fan blades, stator vanes, and frame components. The resulting close proximity of and resulting aerodynamic interaction between the fan blades, stator vanes such as outlet guide vanes and the fan frame requires more than one type of vane in each vane row for achieving desired airflow thereacross. For example, individual vanes of the outlet guide vane row can include various airfoil cross-sections, and pitch, i.e., different airfoil angles of orientation with respect to the turbine radial axis for increasing aerodynamic performance.
The use of non-uniform type airfoils as above described in a turbomachine and the close proximity thereof to adjacent engine components has required a generally more complex mounting assembly in order to provide for the installation and removal of individual airfoils. Such a mounting assembly can include many parts and require accurate manufacturing, and thereby increase the complexity and cost of manufacture and assembly. For example, in order to reduce weight, the mounting members of the assembly are constructed relatively small and additional intravane fairing members are located between adjacent airfoil ends for providing a substantially uninterrupted outer flowpath surface for allowing the smooth flow of gases.
Additionally, turbomachine airfoils are subject to forced excitation at their natural frequencies of vibration which can result in undesirably high airfoil stresses. The stresses are more of a concern when the airfoil members are formed of composite materials. More specifically, the unidirectional strength characteristics of the filaments in an airfoil formed of composite materials adds to the complexity in providing conventional integral shrouds, either at the ends or at part span to mount the airfoil and to accommodate airfoil vibration as has been done with homogeneous metal airfoils.